PREHEAT OVEN TO 350 F. BUTTER OR SPRAY A GLASS LOAF PAN.
IN A SMALL BOWL, WHISK TOGETHER THE FLOUR, BAKING POWDER, SALT, AND SUGAR. SET ASIDE.
IN A LARGE BOWL, WHISK TOGETHER THE EGG, MILK, VANILLA, AND YOGURT OR SOUR CREAM. ADD THE FLOUR MIXTURE TO THE EGG MIXTURE, STIRRING WITH A SPOON JUST UNTIL COMBINED. POUR INTO THE PREPARED LOAF PAN.
IN A SMALL BOWL, STIR THE SWIRL INGREDIENTS TOGETHER. DROP BY TEASPOONFULS ONTO THE TOP OF THE BREAD; THEN USE A KNIFE TO SWIRL IT A COUPLE OF TIMES INTO THE BATTER. (DON’T OVERMIX IT).
BAKE FOR 45-50 MINUTES OR UNTIL THE CENTER TESTS WERE DONE WITH A TOOTHPICK.
REMOVE FROM THE OVEN AND COOL FOR 15 MINUTES IN THE PAN ON A WIRE RACK. REMOVE BREAD FROM THE PAN AND COOL COMPLETELY ON THE RACK.
MAKE THE GLAZE BY WHISKING THE INGREDIENTS TOGETHER IN A SMALL BOWL UNTIL SMOOTH, ADDING A DAB OF MILK AT A TIME UNTIL A GOOD DRIZZLING CONSISTENCY IS REACHED. WHEN THE BREAD IS COMPLETELY COOL, DRIZZLE THE GLAZE